Global tablet sales, led by Apple's iPad, will more than double to 282.7 million in four years as people increasingly shun personal computers in favor of smaller handheld devices, according to tech research firm IDC.

Strong sales of the iPad, as well as new entrants powered by software from Google and Microsoft, prompted IDC to boost its 2016 tablet forecast 8.1 percent from its earlier projection of 261.4 million, the Massachusetts company said.

The growth highlights a transition in the industry as more users turn to tablets for basic computing needs such as browsing the Internet, checking e-mail and watching video, a trend that has hurt sales of traditional PC makers including Hewlett-Packard and Dell. Tablet sales will eclipse those of personal computers by 2015, according to a prediction earlier this year from Boston research firm Yankee Group.

"Tablets continue to captivate consumers, and as the market shifts toward smaller, more mobile screen sizes and lower prices points, we expect demand to accelerate," said Tom Mainelli, tablet research director at IDC, in a statement.

The PC market will shrink by 1.2 percent to 348.7 million sold this year, the first decline in a decade, market researcher IHS iSuppli projected in October. In August, IDC said it anticipated that the PC market would grow less than 1 percent this year and reach 483.1 million by 2016.

Microsoft, which has been battered by the PC slump, introduced its Surface tablet earlier this year. Surface and other handheld machines running Microsoft's Windows operating system will command more than 10 percent of the market by 2016, IDC said. This year, Microsoft's share is 2.9 percent.

The introduction of more tablets, including Surface, Apple's iPad mini and Google's Nexus device, prompted IDC to raise its 2012 forecast 4.4 percent to 122.3 million tablets sold.

As more competitors crowd the market, Apple will lose share to devices using Google's software this year, IDC predicts. Apple's share will slip to 53.8 percent this year from 56.3 percent in 2011, while Google's portion will advance to 42.7 percent from 39.8 percent.

By 2016, Apple will command less than half the market, with 49.7 percent. Google's share will slip to 39.7 percent.

"We continue to see Apple iPad as the dominant tablet," said John Bright, an analyst at Avondale Partners. "The market is growing significantly enough to support multiple competitors."

Shares of Cupertino's Apple fell 6.4 percent to close at $538.79 Wednesday, while Google declined less than 0.5 percent to $687.82.